This invention relates to novel, low cost, brazing preforms, and a method of brazing employed with them. This invention also relates to high strength copper base alloys which may be readily prepared into said preforms to join metal and alloys by the brazing process. Due to the low melting point of these alloys, the resultant brazed joints attain high strength.
For many years the metals industry has used various copper base alloys as brazing media to join other metals and alloys for such applications as electrical motor parts, electrical bus bars, water piping, and tubing systems in air conditioning and refrigeration equipment. The most commonly used filler alloys include the copper-phosphorus alloys, and copper-zinc alloys. The former alloys have low melting points and are brazed at temperatures of 635.degree. to 850.degree.C, while the latter alloys possess higher melting points and are brazed at temperatures of 870.degree. to 950.degree.C.
Concerning the copper-phosphorus alloys, the amount of phosphorus that must be added to copper to sufficiently lower the melting point to a temperature suitable for brazing has a severe embrittling effect on the copper. Thus, these alloys are brittle and can only be fabricated in a limited manner by working when the metal is hot. They are too brittle to be cold worked to any appreciable extent. Thus, they frequently must be applied in a powdered form. Furthermore, the brittle characteristics tend to be carried over to the finished brazed joints made with these alloys. Hence, the copper-phosphorus alloys are limited to use with specific copper base alloys and cannot be used to join ferrous or nickel base alloys.
The copper-zinc brazing alloys containing 40 to 50% zinc, are difficult to fabricate, especially by cold working, because of the beta phase associated with this high zinc content. These alloys possess higher melting points than the foregoing copper-phosphorus alloys and thus must be heated to 870.degree. to 950.degree.C to effect adequate flow into a brazed joint. Extreme caution is necessary to prevent extensive vaporization of zinc from the molten metal, and subsequent void formation in the joint through entrapment of zinc vapor. Because of their poor corrosion and stress corrosion, these alloys find only restricted use to join selected copper base alloys, and stainless steels.
Accordingly, therefore, it is an object of the present invention to provide novel low cost alloys that may be readily and economically fabricated by hot and cold working techniques, into brazing preforms such as thin sheet, strip, or wire, which may be utilized as a media to join copper, ferrous and nickel base alloys by the brazing process.
It is a further object of the present invention to provide brazing preforms which are useful at reduced brazing temperatures and which do not exhibit embrittlement in the resulting brazed joint.
It is a still further object of the present invention to provide sound brazed joints which inherit the high strength, corrosion and stress corrosion characteristics of the filler alloy.
Further objects and advantages of the present invention will appear from the ensuing specification.